Welcome back to my Coursera class, Biochemical Principles of Energy Metabolism. We are in the middle of first week and this is session three. So far, we've started the basic concept of metabolism as well as the concept of energy, the free energy captured in molecules, chemicals. This topic is ATP. What is ATP? ATP is the universal energy currency for the Regardless of the type of organisms or type of cells, even from E.coli like some germs, bacteria and our cells like neurons, our heart muscles, and all types of living organisms utilize ATP as a energy currency, so like coins. This ATP the full name is over here, adenosine triphosphate and you're looking at a ball and stick models. What is adenosine triphosphate? For this session, we are going to review the importance of ATP and the characteristics of ATP. Let me begin with the structure of ATP. We are looking at the chemical structure of ATP. This is adenosine, nitrogen-containing base and this is five carbon sugar, ribose, and there are three phosphate: phosphate one, alpha phosphate, second phosphate from the ribose is beta phosphate, and the most terminal one is gamma phosphate. Adenosine triphosphate, three phosphate in a row. This molecule is the energy molecule for yourselves and for any types of living organisms. What is unique in this structure? Why this molecule can convey, can process the biological energy from this space, from the sugar or fmrom the phosphate? The key is phosphate. When you look at this structure, you have to focus on the negative charge. This phosphate chain contains many of negatively charged ions so that means this ATP's phosphoanhydride bond is very very unstable because too many negatively charged ions concentrated on top of this phosphate tails. When this ATP triphosphate is being hydrolyzed into ADP, adenosine diphosphate, then it means two, right? Only two phosphates and one phosphate is released the most terminal one, gamma phosphate is released. 7.3 kcal/mol of free energy can be dissipated, can be released. That's the point. ATP hydrolysis liberates free energy. Just one phosphate release from ATP can release 7.3 kcal/mol of free energy, which is a lot so such a big energy. This ATP turn over very actively in your cell so total amount of ATP in the human body is only 50 grams, only 50 grams. Think about 50 grams. It's very, very small amount. What does that mean? ATP molecules is constantly recycled. What does that mean? From ATP, ATP, ATP's degraded and then recharged. Minus phosphate, plus phosphate, sometimes ATP can be further degraded into an empty monophosphate and then back. ATP is the carrier and storage unit of free energy and the ultimate source of this ATP production is food. That means high energy containing organic compound, right? Most ATP molecules cannot be synthesized from the very fundamental building blocks. It is generated from ATP by phosphorylation by chemical reaction. The energy used by every adult human being requires the hydrolysis of 100-150 moles of ATP per day. That means 50 to 75 kilograms of ATP supposed to be are newly synthesized each day and that means each ATP molecule is very actively recycled, ATP, ATP, recycled 500-750 times during a day. That means very, very dynamic ATP turn over in a daily life. This is a very unique feature of ATP molecule. Before we get into the real biochemical reactions one by one, I believe we have to fully understand why ATP is so special, why ATP is that important as our energy currency or molecules? The number one reason is ATP hydrolysis and energy coupling. I'm showing a simple biochemical reaction. You are looking at glucose and phosphate and glucose being phosphorylated, glucose six phosphate reaction. This reaction. What is unique in this reaction? This is the first biochemical reaction in terms of glucose metabolism. We are going to study this later, I think week three. The delta G, the change of free energy is positive, positive 14, which there's some more. Then, there's this endergonic the reaction, which is very, very unfavorable and non-spontaneous reaction and definitely stoner energy supposed to be supplied. What about ATP hydrolysis? ATP release phosphate and being converted into ADP and authority one this unit is kilojoule, kilojoule per mole of energy is released, right? ATP hydrolysis is exergonic and spontaneous and favorable reaction. The point is over here. We have two phosphorylate this glucose. We need glucose six phosphate and these two reaction is chemically coupled, biochemical coupled. When these two reaction is coupled, we can write down like this, ATP hydrolyzed into ATP and glucose is being phosphorylated. In terms of free energy changes, we can't just add those two numbers. Plus 14 minus 31. This coupled reaction, the final delta G is minus 17 kJ/mol. Free energy changes of a coupled biochemical reactions are simply additive. Positive on favorable glucose six phosphorylation reaction, throughout is energy coupling via ATP hydrolysis being negative 17 kJ/mol. That means overall reaction now being changed into a favorable biochemical reaction so point is over here. The free energy from the exergonic reaction of ATP hydrolysis can be used to drive thermodynamically unfavorable reaction, in this case, glucose six phosphorylation reaction. As a result, this ATP hydrolysis trigger and facilitate the thermodynamically non-spontaneous reaction into spontaneous reaction. This is the importance of ATP hydrolysis and the unique features of ATP as our energy currency in terms of driving a very unfavorable reaction. This is kind of summary diagram from food molecules throughout a lot of biochemical reaction that we are going to study in the future. ATP is generated and this ATP drive the endergonic reaction and there are many endergonic reactions listed in our cells such as membrane or biosynthesis, protein biosynthesis, nucleic acid production and those reactions so-called biological important polymers. The other way, biologically important macromolecules can be made possible by consuming this ATP and ATP hydrolysis drive this endergonic reactions. Obviously, ATP hydrolysis and the energy coupling is one of the main reasons why ATP is so special in terms of bioenergetics.
